1. Field of the Invention
The present invention relates to a method and a device for removing an injection-molded piece from an injection molding die unit and more particularly relates to a method and a device for removing a plastic shutter of a floppy disk cartridge for housing a recording disk from a die unit.
2. Description of the Related Art
Recording disk units such as a magnetic disk unit, an optical disk unit and a photo-magnetic disk unit have recently been widely used because of the ease and simplicity of handling, high ratio of the storage capacity to the volume, as well as other features thereof.
FIG. 5 illustrates a floppy disk unit 1 which is typically used for disks which are 3.5 inches in diameter. The unit 1 includes upper and lower square half cartridge bodies 2 and 3, which are injection-molded of an ABS resin or the like, an annular center plate 4, and a magnetic disk 5 rotatably supported inside the cartridge bodies. The disk 5 is a magnetic flexible medium made of a circular film of a high-molecular substance with a magnetic layer uniformly provided on the surface of the film. The center plate 4 is fixedly fitted in the circular center hole of the disk 5. The central portion of the lower half cartridge body 3 has an opening 7 formed therein through which the shaft of a motor is to be inserted into the square hole 6 of the central portion of the center plate 4. The front portions of the half cartridge bodies 2 and 3 have magnetic head insertion slots 8 formed therein through which a magnetic head and a head support are to be inserted into the unit 1 to write or read information into or from the disk 5.
The unit 1 also includes a slide shutter 20 fitted on the half cartridge bodies 2 and 3 so that the shutter can be slid to uncover the magnetic head insertion slots 8 of the bodies or cover same to prevent dust or the like from entering into the unit through the insertion slots 8 and from clinging to the magnetic disk 5. The shutter 20 is a U-shaped thin metal sheet such as a stainless steel sheet, and has a projection formed near the central portion thereof which is fitted in a guide groove formed in the outer part of the front portion of the lower half cartridge body 3. The projection can be slid in the groove in such directions as to cover and uncover slots 8 of the bodies 2 and 3. The range 11 of the sliding of the shutter 20 covers the slots 8, and extends on an area of each side surface of the whole cartridge body of the unit 1. The shutter 20 has apertures 10 formed therein so that when the unit 1 is in use, the apertures 10 coincide with the magnetic head insertion slots 8 of the half cartridge bodies 2 and 3 to expose the disk 5 to make it possible to insert the magnetic head and the head support into the magnetic head insertion slots 8 toward the disk. When the unit is not in use, the apertures 10 do not coincide with the magnetic head insertion slots 8 and the shutter closes the magnetic head insertion slots 8 to cover the disk as shown by the two-dot chain line in FIG. 5.
It has recently been proposed that such a slide shutter may be injection-molded of a synthetic resin to reduce the labor and cost necessary for manufacturing the shutter. Japanese Patent Applications (OPI) Nos. 231985/85 and 70981/89 disclose such a device (the term "OPI" as used herein means an unexamined published application"). Generally, a self-lubricating crystalline plastic such as polyacetal is used as the synthetic resin to attain a satisfactory shutter. The temperature of a molding die unit for the injection molding of the shutter is required to be high enough, 70.degree. to 90.degree. C. normally, to grow the crystal grains of the plastic. For that reason, the temperature of the shutter when removed from the die unit immediately after the injection molding is as high as 80.degree. to 100.degree. C.
Since the temperature of the slide shutter when removed from the die unit immediately after the injection molding of the shutter is so high, the shutter can be easily deformed by a low external force. Therefore, it is necessary to exercise great care during removal which makes the removal operation very difficult. The slide shutter can be injection-molded either in a horizontal posture or in a vertical posture inside the die unit. However, it is desirable, because of the stability of the movement of the dies of the die unit and shorter time of removal, to injection-mold the shutter in the vertical posture inside the die unit as shown in FIGS. 6 and 7.
As shown in FIG. 6, the mutually meeting portions of the right and left dies a and b of the die unit have projections 3 and 3a positioned so as to be located near the upper and lower portions of the shutter 20 when it is injection-molded in the vertical posture inside the die unit. After the injection process, the shutter 20 is thrust out from the die unit by upper and lower thrust pins 2, 2 and the right and the left dies a and b are moved apart as indicated by arrows in FIG. 6. As a result of the movement of projections 3a of the left die b, open spaces are left above and below the shutter 20 so that the shutter is not supported at the upper and lower portions thereof by the right and the left dies, but is supported only by the core c of the die unit. For that reason, the shutter 20 tends to tilt as illustrated in FIG. 7. Accordingly, the shutter sometimes drops while being thrust out from the die unit by the pins 2. This can damage the shutter. The tilting also may cause the gas vent portions of the right die a, which are located near the projections 3 of the die, to be contaminated by the resin of the shutter 20. Also, the shutter 20 is more likely to interfere with mechanisms used in the manufacturing process while being conveyed to a next step of processing when its position deviates from a desired position.